Disruption of sleep recovery after 36 hours of exposure to moderately bright light

Eight young adults were exposed to either 36 hours of moderate bright light (BL; 1,000-2,000 lux) or a light/dark cycle (L/D <50 lux) during constant routine. Sleep was recorded on the two subsequent recovery sleeps (Rl and R2) and compared to baseline. After the BL exposure, the rebound of stage 4 sleep and slow wave activity (SWA) were split over R I and R2, whereas after the L/D cycle, the stage 4 sleep debt was almost completely compensated for during Rl. During Rl, stage 2 sleep and wakefulness accumulated faster in the BL condition than in the L/D condition. An elevation of the temperature level was also found during Rl of the BL condition. No differences between light conditions were found in urinary levels of melatonin or cortisol secreted during Rl or R2. Homeostasic process does not appear to be affected by the BL condition. A modification in the sleep wake balance and a change in the temporal relationship between the circadian system and the sleep-wake cycle are discussed.